1. Field of the Invention
This invention relates to hydrocarbon hydroprocessing catalysts, such as those utilized to catalyze the reaction of hydrogen with organo-nitrogen, organo-metallic and particularly organo-sulfur compounds. More particularly this invention is directed to a catalyst useful for the hydrodesulfurization of hydrocarbons, such as residuum oils, and to a method for preparing such catalysts by employing an aqueous impregnating solution with porous, amorphous refractory oxide support particles. The invention is especially directed to catalysts of high overall desulfurization activity.
2. Description of the Prior Art
In the refining of hydrocarbons, it is often necessary to convert a hydrocarbon-containing oil fraction to different forms. Typically, particulate catalysts are utilized to promote desulfurization, denitrogenation or demetallization reactions when feedstocks such as residuum-containing oils are contacted with catalysts under conditions of elevated temperature and pressure and in the presence of hydrogen so that the sulfur components are converted to hydrogen sulfide, the nitrogen components to ammonia and the metals are deposited on the catalyst.
Hydroprocessing of hydrocarbon-containing oils may be carried out with a catalyst containing Group VIB and Group VIII hydrogenation metals on a refractory oxide support. Compositions containing these and other elements have been previously prepared by comulling and impregnation methods. For example, catalysts useful for hydroprocessing residuum-containing oils comprising a Group VIB metal, particularly molybdenum or tungsten, and a Group VIII metal, particularly cobalt or nickel, on an alumina base have been disclosed in U.S. Pat. Nos. 3,980,552, and 4,460,707. In U.S. Pat. No. 3,980,552, a catalyst having an average pore diameter between 40 and 100 angstroms is prepared by comulling precursors of the hydrogenation metals with those of the support materials. The catalyst in U.S. Pat. No. 4,460,707 has an average pore diameter greater than about 180 angstroms and is prepared by impregnation, that is, by deposition of the active components on the support base by contact thereof with an aqueous solution containing the hydrogenation components in dissolved form. Such catalysts have been previously effective for removing contaminant metals and sulfur from residuum-containing oils.
Although conventional catalysts are active and stable for hydrocarbon hydroprocessing reactions, catalysts of yet higher activities and stabilities are still being sought. Increasing the activity of a catalyst increases the rate at which a chemical reaction proceeds under given conditions, and increasing the stability of a catalyst increases its resistance to deactivation, that is, the useful life of the catalyst is extended. In general, as the activity of a catalyst is increased, the conditions required to produce a given end product, such as a hydrocarbon of given sulfur, nitrogen, and/or contaminant metals content, become more mild. Milder conditions require less energy to achieve the desired product, and catalyst life is extended due to such factors as lower coke formation or the deposition of less metals.